Improvement in processes for treating auriferous and argentiferous sulphurets



UNITED STATES PATENT OFFICE.

HOMER HOLLAND, OF WESTFIELD, MASSACHUSETTS.

Specification forming part of Letters Patent No. l 2,94 5, dated May 29, 1855.

phurets is the nitrate of soda-an article, 1 be"- lieve, not hitherto employed in any process of dry assaying,and oneof which I have found no mention in any work orftreatise on metallurgy. The nitrate of potash, which in its general chemical character somewhat resembles the nitrateof soda, has heretofore been-used in a single crystal"forblow-pipe testing, and to.

'scarify and oxidize in remelting gold and sil ver inzthe crucible; but it is utterly impracti cable in any hitherto recognized process for separating gold and silver fromthe sulphurets on a larger scale, since it readily ignites, 'and its combustion is so violent and explosive as to eject, the matter from the crucible, while the heat that it generates is so intense as to volatilize a portion of the metals subjected to its influence; and, indeed, the use of the nitrateof potash, even indry crucible assays, is now,

according to the best authorities, obsolete. But on the other hand I have discovered, and through my process am able to make use of, certain properties in the nitrate of soda which render it highly useful in the disintegration and resolution of metalliferous sulphuret-s, and which show-that. it is very difi'erent in its action from the nitrate of potash. Unlike the last-mentioned salt, the nitrate of soda, when ignited, burns slowly and mildly, and more especially so with the metallife'rons sulphurets, while there is also neither violent action to explode and scatter the mixture,nor heat generated sufticientlyintense to volatilize the metals. This hitherto unrecognized difference in the action of the nitrate of potash and the hitrate of soda on metallil'erous sulphurets isthe property which I make use of in my invention, and which I believe to'be clearly distinguishable from all processes hitherto adopted, for although it consists in part of so well known a material as the nitrate of soda, yet this material is so combined with and proportioned to the ores acted upon by the method persued in my process as to give to the practical metallurgist advantages essentially different from those he can obtain by any other method practiced for the dry assaying of the precious met als.

The manner in which my process is conducted is as follows: A'quantity of the nitrate of soda asfree as possible from any admixture with other salts is provided, togetherwvith a quantity of any metalliferous sulphuret, both being separately or jointly finely 'pulveri'zedby means of Bogarduss eccentric mill or any other suitable mechanical contrivance, and then thoroughly mixed together in a dry state in theproportion of two hundred and ninetyone parts of the nitrate of sodato' every hun dred parts of the sulphur previously dete'i' mined and known to exist in the ore to be operated upon; About one-third part of this mixture must then be deflagrated in a large cast-iron basin having aconcave soleorhearth, like that of a Glausthal cupel, heated from he neath to moderate redness, a'nda-t separate intervals of about half an hour each'the remain ing two-thirds are to be added while the mass in the basin is being thoroughly stirred and intermixed. Then the heat, moderate at first, is gradually to be increased until the sulphurous-acid vapors have entirely passed-oh, and full oxidation and redness of the ores are ob; tained. When cooled'down the silver or gold, or both, previouslyzcontained in the ore will be found reduced to fine grains or particles, which may be readilyseparated by means of a con- -centrator, or amalgamated by mercury from theresolved anddecomposed mass in the same manner as from any other aurife'rous and argentiferous sands or oxides. In soineinstances, however, andmore especially in treating the bisulphure'ts, it \vill be found expedient to subject the pulverized ore to a preliminary roasting, in order to expel in an acid form some'portion of the sulphur, by. which means a certain amount of the nitrate of soda will be saved in the operation; and consequently I do not and cannot in any way restrict myself to any precise'ratio of the proportions of the sen eral ores and nitrate of soda, since a greater or less proportion of the salt will, under difi erentcircumstances, to a certain extent, effect the decomposition required. An rexcess can in no instance whatever'either injure the process or yitiate the result, nor can likewise the degree of transmitted heat, provided, always,it be moderate at first and increased gradually. Neither is it absolutely necessary .that in all cases the nitrate of soda should be mixedlhefore roasting wit-hthe ore,since in some instances it may be found advantageous to gradually stir it in while the ore is being roasted.

When coppcrpyrites are decomposed and resolved by my process, it will be found advantageous. to lixiviate the cooled mass with water, so as to dissolve the sulphate of copper,

which other-wise would attack the mercury used in amalgamating the gold or silver. Having now described and particularly set forththe nature of myinvention and the manne-rin which the same is or may be used or carriedintopflect. I would observe, in conclu- "2 teens In witness whereof I, the said HOMER HOL- LANmh ave hereunto set my hand and seal this 7th day of May', 1855.

HOMER HOLLAND n s.]

Witnesses:

STAFFORD REEVES, J. WINcansrEs. 

